The objectives of this study are to define the roles of basement membrane proteoglycans in the regulation of mammary epithelial cell differentiation. Their influence on cell attachment and morphology will also be studied. In the long term it is expected that the investigations will contribute to a better general understanding of the role of basement membranes in differentiation and development. In addition, the study should help define some of the unknown functions of proteoglycans in epithelial tissue, and reveal some of the basic functions of these ubiquitous molecules. Experiments will be carried out using cultures of mouse mammary epithelial cells isolated from late pregnant mice and a recently isolated mouse mammary epithelial cell line, COMMA-1-D. When cultured on a suitable substratum, namely floating collagen (type I) gels, the cells synthesise many milk proteins and also assemble a distinct basement membrane. As such they constitute an experimental system that can be readily modulated. Three approaches to the problem will be pursued: 1. p-Nitrophenyl-Beta-xyloside, a highly specific inhibitor of proteoglycan synthesis will be used to perturb proteoglycan and glycosaminoglycan metabolism and the consequential changes in cellular differentiation monitored by following milk protein synthesis. 2. Cells will be cultured on purified proteoglycans and on proteoglycans complexed to other basement membrane components (rather than stromal matrix components). Again their effects will be assessed by examining milk protein synthesis. 3. Monoclonal antibodies will be produced against purified basement membrane proteoglycans and will be used in immunocytochemical experiments to study the relationship between basement membrane proteoglycan composition and epithelial cell differentiation in the developing gland itself. It is expected that this study will shed light on some basic mechanisms controlling cell differentiation and cell physiology. However, the information should also be important for tumor biology in that alterations of glycosaminoglycan metabolism and cellular differentiation both frequently occur in tumor development. Whether or not these two parameters are interrelated in normal cellular processes is thus likely to be of considerable interest to tumor biology.